The optomotor response has been widely used to
investigate insect sensitivity to contrast and motion. Several
studies have revealed the sensitivity of this response
to frequency and contrast, but we know less about the
spatial integration underlying this response. Specifically,
few studies have investigated how the horizontal angular
extent of stimuli influences the optomotor response. We
presented mantises with moving gratings of varying horizontal
extents at three different contrasts in the central or
peripheral regions of their visual fields. We assessed the
relative effectivity of different regions to elicit the optomotor
response and modelled the dependency of the response
on the angular extent subtended by stimuli at these different
regions. Our results show that the optomotor response
is governed by stimuli in the central visual field and not
in the periphery. The model also shows that in the central
region, the probability of response increases linearly with
increase in horizontal extent up to a saturation point. Furthermore,
the dependency of the optomotor response on the
angular extent of the stimulus is modulated by contrast. We
discuss the implications of our results for different modes
of stimulus presentation and for models of the underlying
mechanisms of motion detection in the mantis.